THE SYNTHESIS AND TRANSITION-TEMPERATURES OF SOME DIFLUORO-SUBSTITUTED CYCLOHEXANES

A range of trans-1,4-disubstituted cyclohexane materials has been prep ared that incorporates a difluoromethylene unit as part of the cyclohe xane ring. These compounds illustrate the great difference in mesogeni c behaviour between compounds with fluoro-substituents in an alicyclic environment and those with fluoro-substituents in aromatic rings. An improved fluorination method, which involves the use of hydrogen fluor ide-pyridine, has been developed and provides high yields of fluorinat ed materials. Highly efficient palladium-catalysed cross-coupling reac tions involving arylboronic acids have been used to provide the final liquid crystal materials. The important issue of the cis and trans iso mers of these compounds is discussed and the structures of the fluorin ated materials are discussed with reference to their interesting H-1 a nd C-13 NMR spectra.